This invention relates to industrial fuels and chemicals, and in particular to an improved process for the removal of lignin-derived phenolic compounds from dissolved sugars in an aqueous biomass hydrolyzate and the biological conversion of the sugars into fuels and chemicals.
As is well known in the biological conversion art, the traditional method for detoxifying a biomass hydrolyzate liquor is overliming. Overliming has been widely used since the 1940""s. Leonard, R. H. and Hajny, G. J. Fermentation of Wood Sugars to Ethyl Alcohol, Industrial and Engineering Chemistry, vol.37, No. 4, p.p. 390-395 (1945). The basic steps in the overliming process include: adjusting the pH of the hydrolyzate to 10.0xc2x10.1 using Ca(OH)2 or lime, heating the hydrolyzate to 60xc2x0 C. for 30 minutes, filtering the heated hydrolyzate to remove precipitated solids, and acidifying the filtrate to a pH optimum, which is efficient for the bio-conversion of the dissolved sugars into the desired product(s).
A distinct disadvantage of the overliming process is the difficulty in controlling the pH adjustment step. Where a fermentable substrate is a dissolved sugar, strict control over the pH adjustment step is critical because, at a pH greater than 10 one experiences a degradation in the fermentable carbohydrate fraction. It is a further disadvantage in that the mechanism of overliming is not well understood, thereby making it difficult to optimize the process. Moreover, overliming does not detoxify hydrolysis liquors to the extent that an undiluted hydrolyzate comprises an efficient fermentable substrate (overliming allows fermentation at 30%-50% liquor concentration). It is also desirable, in some overliming applications, to use less lime, thereby resulting in the production of less insoluble gypsum, which has been found to precipitate in process lines.
Therefore, it is an object of the invention to provide a process for converting a biomass hydrolyzate into fuels or chemicals using a microbial culture.
It is a further object of the invention to provide a process for detoxifying a biomass hydrolyzate for use as a conversion substrate.
It is still a further object of the invention to provide a process of converting a hydrolysis liquor without first diluting the liquor as a component of the medium.
It is yet another object of the invention to improve the product yield in a microbial chemostat process for converting a biomass hydrolyzate into fuels and chemicals, such as ethanol or lactic acid.
Briefly, the invention provides a process of making a fuel or chemical from a biomass hydrolyzate comprising the steps of providing a biomass hydrolyzate, adjusting pH of the hydrolyzate, contacting a metal oxide having an affinity for guaiacyl or syringyl functional groups or both, and the hydrolyzate for a time sufficient to form an adsorption complex; removing the complex wherein a fermentable sugar fraction is provided, and converting the sugar fraction into a fuel or chemical using a microorganism.
The foregoing specific objects and advantages of the invention are illustrative of those which can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages which can be realized. Thus, those and other objects and advantages of the invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variations which may be apparent to those skilled in the art.